A process is operable using a computerized system for grading the colour of a diamond using a pre-trained neural network for determination of a colour grading. The computerized system includes an optical image acquisition device, a pre-trained neural network and an output module operably interconnected together via a communication link. The process includes: (i) acquiring via an optical image acquisition device one or more optical image of at least a portion of a diamond; and (ii) in a pre-trained neural network, providing a regressive value associated with the colour grade of the diamond.